The glutathione S-transferases (GSTs) are a superfamily of ubiquitously expressed enzymes that conjugate reduced glutathione (GSH) with toxic electrophiles. The GST isoforms have also been show to regulate ASK-1 and JNK activation via protein-protein interactions. In human populations, the GST isoforms are distributed in a race- and gender-specific manner. The GSTs are expressed in cardiovascular tissues, but the role of GST in cardiovascular physiology and pathology has not been studied. We propose that GSTP, the most abundant cardiac isoform, is an essential component of myocardial defense against oxidative stress and it protects the heart from acute oxidative damage during ischemia-reperfusion (I/R). To test this hypothesis, we will assess the contribution of GSTP to cardiac protection during I/R in situ (Aim 1), metabolism of lipid peroxidation- derived aldehydes (acrolein and 4-hydroxy-trans-2-nonenal; HNE), which are the preferred endogenous substrates of this enzyme (Aim 2), and aldehyde detoxication (Aim 3). As a loss of function test, GSTP-null mice will be exposed to I/R, while in gain of function tests, transgenic (TG) and TG mice crossed with null mice with cardiac-restricted expression of human polymorphic GSTP1-1 genes will be exposed to I/R and infarction determined. Using tracer kinetics and mass spectrometric analysis, we will measure the extent to which glutathiolation accounts for the metabolism of these aldehydes before, during and after ischemia in the heart (Aim 2). To delineate the contribution of GSTP, we will compare metabolic pathways, including aldehyde conjugation and peroxidase activity, in hearts isolated of GSTP WT, null, and TG mice. In Aim 3, we will determine whether GSTP protects the heart from I/R-induced injury by increasing glutathione conjugation of aldehydes, decreasing aldehyde formation, decreasing aldehyde-protein adducts, decreasing peroxide formation, decreasing oxidative post-translation protein modifications (e.g., sulfenic acid) by glutathiolation, and protecting myocardial GSH level. In addition, we will determine if GSTP regulates JNK activation and JNK signaling thereby investigating a non-catalytic role of GSTP in protein-protein interactions. Successful completion of these studies may lead to the identification of a novel mechanism of cardioprotection by GSTP, which may be useful in assessing the relative ischemic susceptibility of human populations polymorphic in GSTP and in developing more targeted anti-ischemic interventions. PUBLIC HEALTH RELEVANCE The glutathione S-transferases (GSTs) are widely expressed enzymes that detoxify reactive compounds. In human populations, the GSTs are distributed in a race- and gender-specific manner, and GST polymorphisms are associated with increased cardiovascular disease risk. This study will assess if GSTP is an essential component of myocardial defense against injury of heart attacks. Successful completion of these studies may lead to the identification of a novel mechanism of cardioprotection by GSTP, which may be useful in understanding the relative susceptibility of human populations polymorphic in GSTP to coronary heart disease and in developing more targeted cardioprotective interventions.